The present invention relates to a method of controlling a head in an image recording apparatus for forming an image as a set of pixels as minimum units and recording the pixels on the basis of image information of each pixel, the method performing gradation expressions of each pixel in accordance with a change in a recording area and/or a recording density.
An ink spray type image recording apparatus employing a spray gun type head is known as a conventional image recording apparatus of this type. This image recording apparatus employs a method of controlling a valve mechanism of the spray gun type head to adjust an air flow rate, thereby varying a siphon effect rate to change an ink injection amount (discharge amount). That is, an ink density in the sprayed air is changed to change a density of an ink (i.e., a recording density of a pixel) sprayed onto recording paper or the like, thereby performing gradation expressions.
In the conventional image recording apparatus of this type, however, since its head comprises a siphon type spray gun having a solenoid valve, the unit including the valve body is heavy and is not easy to handle. An operation amount of the head is increased to degrade the response characteristics. In addition, an ink amount is controlled through air as a compressive fluid, and the response characteristics are further degraded. As a result, reproducibility of image information is degraded. The structure of the head is complicated, and complicated adjustment and maintenance require much labor and skills.